This invention relates to the polymerization of olefins by the coordinate complex method, often termed the Ziegler-Natta method after the names of the two workers who contributed so muct to its practical development and theoretical basis. More particularly, this invention relates to novel, activated supports for the transition metal catalytic component.
About 30 years ago the original Ziegler-Natta catalysts were heterogeneous slurries formed in place when solutions of organometallic cocatalysts, preferably taken from the compounds of metals of Groups IA, IIA, and IIIA of the periodic table, were added to solutions of transitional metal catalysts, preferably taken from compounds of metals of Groups IIIB, IVB, and VB of the periodic table. These catalytic systems by today's standards did not have high activity in terms of grams polyolefins produced per gram catalyst component. Nor, when propylene or other monomers capable of giving polymers with tacticity were employed, did these early catalytic systems provide polymer with high isotactic index. Also, the particle size distribution of the polyolefin was too broad, leading to an undesirable fraction of "fines", particles less than about 100-180 .mu.m.
More recently, high activity, high isotactic index, and enhanced particle size have been achieved by employing catalyst supports on which catalytic transition metals have been dispersed. It has been theorized that the concentration of active polymerization centers is as much as 50 percent higher on supported catalysts than unsupported catalyst systems. These developments are discussed in the Kirk-Othmer "Encyclopedia of Chemical Technology", third edition, vol. 16, pp. 453-469 in an article entitled Olefin Polymers (Polypropylene) and in Angewandte Makromolekulare Chemie, 94, 63-89 (1981). One support which has gained favor in technical circles is magnesium halide, particularly in an activated condition. The preferred method for activating catalyst support such as magnesium halide is dry milling, as disclosed in British Pat. No. 1,335,887.
Dry milling suffers from many practical defects. Among these are long milling regimes, losses of support by "hold-up" in the milling equipment, excessive handling, the cost of milling energy, and a wide dispersion of the particle size of the milled products leading to excessively broad particle size distribution of the polyolefin. It would be advantageous to have the high catalytic activity of a supported catalyst, the high isotacticity of polymers capable of such (e.g., polypropylene) and a decreased proportion of "fines" without the necessity of a milling or grinding step. This is achieved by use of the present invention.
U.S. Pat. No. 4,329,253 discloses procedures for preparing a catalytic component for polymerizing olefins wherein commercial magnesium alkoxides or magnesium alkoxides generated in situ from the metal plus alcohol are treated with an electron donor and titanium tetrachloride (TiCl.sub.4) to form a solid, which is always further treated with a halocarbon or halogenated hydrocarbon plus post-treatment with TiCl.sub.4.
Japanese patent application No. 80/23,435, published as JP 81/120,711 (C.A. 96:20578e) discloses combining magnesium ethoxide with tetrabutyl titanate in heptane to produce a solid. This solid is then further treated with ethyl benzoate and TiCl.sub.4 to yield a catalytic component for polymerizing olefins.
Japanese patent application No. 79/150,026 published as JP 81/74,103 (C.A. 95:133633s) discloses a process for heating magnesium ethoxide with ethanol and TiCl.sub.4 to form a solid. This solid is then further treated successively with ethyl benzoate, tetraethyl silicate and TiCl.sub.4 to produce a catalytic component.
Japanese patent application No. 80/1,266, published as JP 81/99,207 (C.A. 95:204706f) discloses a process for preparing a catalytic component for polymerizing olefins by refluxing magnesium ethoxide with isopropyl alcohol and silicon tetrachloride to produce a solid. This solid is then successively treated with ethyl benzoate and boiling TiCl.sub.4 to yield a catalytic component for polymerizing propylene.